The back pain caused by a damaged intervertebral disc often requires surgery, which means either replacing the disc with a plastic or metal implant or removing the disc and fusing the adjacent ones together. A new type of replacement disc—consisting of a scaffold seeded with living cells—could relieve back pain without many of the side effects caused by existing surgical approaches.
Researchers at the Medical University of South Carolina made a prototype replacement disc by printing an outer scaffold and then seeding the scaffold with living cells. The scaffold closely mimics the intricately layered microstructure of a real intervertebral disc, and is the first step toward making an implant that can perform the same supportive and shock absorbing functions as the original.Compared to the metal and plastic implants used today, an artificial scaffold swathed in living tissue could repair itself, and constant access to blood supply would reduce the risk of infection after surgery.
An intervertebral disc, or IVD, is shaped like a jelly donut, with an soft, elastic center and a tougher, fibrous outer layer. Sandwiched between vertebrae in the spine, the disc defines and supports the spine’s movement, holding bones in place while allowing the spine as a whole to bend and twist. The discs also act as shock absorbers, cushioning impacts to the spine. When a disc becomes worn, pressure along the spine is unevenly distributed, and if the vertebrae shift even slightly, they stretch the nerves circling the spine, causing pain. If exercise and physical therapy offer no relief, surgery may be required.
Spinal fusing, however, restricts bending and twisting in the fused section of the spine, so some surgeons make a strong case for the implant method. “None of us were born with fused spines,” says Barton Sachs, a professor of orthopedics at the Medical College of South Carolina, who routinely performs disc-implant surgery and who was not connected with the new work. Fusing two bones together can increase the pressure on neighboring segments, wearing out other discs, Sachs says. Not only does an implant preserve motion, but the recovery time from implant surgery is shorter. “It works extremely well,” says Sachs. “[Patients] get out of the hospital faster; they get back to their lifestyles faster.”
But the implants currently used do not absorb shock. “You’re putting in materials that look medieval, and that’s the state of current clinical practice,” says Robert Mauck, professor of orthopedic surgery and tissue engineering at the University of Pennsylvania. Mauck is working on a competing improvement to disc implants.